Lactic acid (2-hydroxypropanoic acid, 2-hydroxypropionic acid) is an organic hydroxy acid whose occurrence is widespread. It was first produced commercially in the United States in 1881 and has been in continuous production here since 1894. Concentrated whey has been used as a feedstock for producing lactic acid in the United States since 1936.
Lactic acid has two stereoisomeric forms: L-(+)-lactic acid and D-(-)-lactic acid. For certain applications, such as production of poly(lactic acid) and other lactic acid polymers, stereoisometrically pure lactic acid is required. Present commercial fermentation processes produce a mixture of stereoisomers. Since the stereoisomers are very difficult to separate, a need exists for an inexpensive fermentation process for producing a single stereoisomer of lactic acid.